---
title: Complexity plugin
description: Complexity plugin docs for Pothos
---

This plugin allows you to define complexity of fields and limit the maximum complexity, depth, and
breadth of queries.

## Usage

### Install

```package-install
npm install --save @pothos/plugin-complexity
```

### Setup

```typescript
import ComplexityPlugin from '@pothos/plugin-complexity';

const builder = new SchemaBuilder({
  plugins: [ComplexityPlugin],
});
```

### Configure defaults and limits

To limit query complexity you can specify a maximum complexity either in the builder setup, or when
building the schema:

```typescript
const builder = new SchemaBuilder({
  plugins: [ComplexityPlugin],

  complexity: {
    defaultComplexity: 1,
    defaultListMultiplier: 10,
    limit: {
      complexity: 500,
      depth: 10,
      breadth: 50,
    },
    // or
    limit: (ctx) => ({
      complexity: 500,
      depth: 10,
      breadth: 50,
    }),
  },
});
// or
const schema = builder.toSchema({
  complexity: {
    limit: {
      complexity: 500,
      depth: 10,
      breadth: 50,
    },
  },
});
```

#### Options

- fieldComplexity: (optional,
  `(args, ctx, field) => { complexity: number, multiplier: number} | number`): default complexity
  calculation for fields. `defaultComplexity` and `defaultListMultiplier` will not be used if this
  is set.
- defaultComplexity: (optional `number`) defines the default complexity for every field in the
  schema
- defaultListMultiplier: (optional `number`) defines a default complexity multiplier for a list
  fields sub selections
- limit: Defines limits for queries, passed the context object if `limit` is a function
  - complexity: defines the maximum complexity allowed for queries
  - depth: defines the maximum depth of selections in a query
  - breadth: defines the maximum total selections in a query
- complexityError: (optional `function`) defines the error to throw when the query complexity
  exceeds the limit. The function is passed the errorKind (depth, breadth, or complexity), the
  result (with the depth, breadth, complext, and max values), and a GraphQL `info` object. It should
  return (or throw) an error, or a an error message as a string

### How complexity is calculated

Complexity is calculated before resolving root any root level fields (query, mutation,
subscription), and is based purely on the shape of the query before execution begins.

The complexity of a query is the sum of the complexity of each selected field. If a field has
sub-selections, the complexity of its sub-selections are multiplied by a fields multiplier, and then
added to the fields own complexity. The default multiplier for fields is 1, and 10 for list fields.
This multiplier is meant to the n+1 complexity of list fields.

#### Example

The following query has a complexity of `131` (assuming we are using the default options), a depth
of `3`, and a breadth of `5`:

```gql
query {
  posts {
    # complexity = 131 (posts + 10 * (2 + 11))
    author {
      # complexity = 2 (author + 1 * name)
      name # complexity = 1, depth: 3
    }
    comments {
      # complexity = 11 (comments + 10 * comment)
      comment # complexity = 1, depth: 3
    }
  }
}
```

### Defining complexity of a field:

You can set a custom complexity value on any field:

```typescript
builder.queryFields((t) => ({
  posts: t.field({
    type: [Post],
    complexity: 20,
  }),
}));
```

The complexity option can also set the multiplier for a field:

```typescript
builder.queryFields((t) => ({
  posts: t.field({
    type: [Post],
    complexity: { field: 5, multiplier: 20 },
  }),
}));
```

A fields complexity can also be based on the fields arguments, or the context value:

```typescript
builder.queryFields((t) => ({
  posts: t.field({
    type: [Post],
    args: {
      limit: t.arg.int(),
    },
    // base multiplier on how many posts are being requested
    complexity: (args, ctx) => ({ field: 5, multiplier: args.limit ?? 5 }),
  }),
}));
```

## Utilities

### `complexityFromQuery(query, options)`

Returns the query complexity for a given GraphQL query.

```typescript
const complexity = complexityFromQuery(query, {
  schema: schema,
  // Complexity can be calculated based on the context and arguments,
  // so you may need to provide valid values for the context and arguments.
  // Both are optional, and will default to empty objects.
  context: {},
  variables: {},
});
```
